Method and apparatus for coupling light-emitting elements with light-converting material

ABSTRACT

Light-emitting elements such as LEDs are associated with light-converting material such as phosphor and/or other material. A donor substrate comprising the light-converting and/or other material is suitably placed relative to a target substrate associated with the light-emitting elements. A laser or other energy source is then used to transfer the light-converting and/or other material in a pattern via writing or masking from the donor substrate to the target substrate in accordance with the pattern. Addressability and targetability of the transfer process facilitates precise patterning of the target substrate.

CLAIM OF PRIORITY

This application claims priority under 35 USC §120 to U.S. patentapplication Ser. No. 13/205,572, filed on Aug. 8, 2011, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present technology pertains in general to manufacturing ofsolid-state lighting devices and in particular to methods and apparatusfor coupling solid-state light-emitting elements such as LEDs withlight-converting materials such as phosphors.

BACKGROUND

Solid-state lighting devices such as light-emitting diodes (LEDs) canprovide for efficient and versatile light sources. Characteristics, ofthe light emitted by such lighting devices, such as chromaticity, can beadjusted by utilizing light-converting materials, such as phosphors. Asan example, white light LEDs can be manufactured by applying a yellowemitting phosphor coating to a blue or ultraviolet “pump” LED,respectively. Light from the pump LED is absorbed by the phosphor,causing the phosphor to re-emit light at a different characteristicwavelength. The perceived colour of combined light from the LED andphosphor coating may thus be adjusted to a desired white. A variety ofmethods for providing light of a desired chromaticity are known.

The reliable manufacture of lighting devices utilizing solid-state lightsources in combination with light-converting materials faces severalchallenges. Firstly, light-emitting elements such as LEDs typicallyexhibit substantial variation in chromaticity and other characteristics,both within and between manufacturing batches. Secondly, properties oflight-converting material as well as the disposed quantities thereofexhibit fluctuations that can be poorly controlled in conventionalmanufacturing processes. Conventional manufacturing processes usuallydispense phosphors suspended in a binder solution of silicone into acavity engulfing the LED(s), thereby providing limited control overcomposition and disposition of adequate amounts of phosphors. Suchprocesses consequently provide poor control over conversion efficiencyand chromaticity variations of the generated light. Moreover, unusedbinder solution typically ends up as waste because recycling ofphosphors from typical binder solutions is prohibitively expensive.Typically, manufacturing costs are therefore unnecessarily high whenphosphors are wasted that include expensive rare earth elements.

As a result, existing methods for producing solid-state lighting devicesincorporating light-converting materials can exhibit significantvariation. For example, existing bulk manufacturing processes forproducing white phosphor coated LEDs typically provide LEDs which maysignificantly and perceptibly vary with respect to chromaticity, whichnecessitates testing and binning of the LEDs. Manufacturing yields arethus reduced by variations in the source materials and variations due tothe phosphor coating process. Therefore, there is a need for a methodand apparatus for coupling solid-state light-emitting elements withlight-converting materials that is not subject to one or more of theabove limitations.

U.S. Pat. No. 5,521,035 discloses methods for preparing color filterelements using laser induced transfer of colorants with associatedliquid crystal display devices. Color filter elements are prepared bythe laser-induced transfer of colorant from a color donor to atransparent, non-birefringent substrate such as glass or polymeric film.

U.S. Pat. No. 5,171,650 discloses a method and system for creating andtransferring a pattern from a composite ablation-transfer imaging mediumto a receptor element in contiguous registration therewith. The methodis applicable for color proofing and printing, security coding, graphicarts and printed circuit industries. The composite imaging mediumcomprises a support substrate, one or more dynamic release layers, andan imaging radiation-ablative carrier topcoat, which includes an imagingamount of a contrast imaging material. The dynamic release layer absorbsradiation to effect the imagewise ablation mass transfer of the carriertopcoat.

U.S. Pat. No. 7,153,618 discloses a method of forming a color filtersubstrate of a liquid crystal display device. A black matrix is formedon a substrate, a color filter transfer film is attached to thesubstrate, and a laser beam is used to irradiate the entirety of thecolor filter transfer film. The color filter transfer film includes red,green and blue color filter patterns. The transfer film is removed fromthe substrate such that the red, green and blue color filter patternsremain on the substrate.

This background information is provided for the purpose of making knowninformation believed by the applicant to be of possible relevance to thepresent technology. No admission is necessarily intended, nor should beconstrued, that any of the preceding information constitutes prior artagainst the present technology.

SUMMARY OF THE TECHNOLOGY

An object of the present technology is to provide a method and apparatusfor coupling light-emitting elements with one or more light-convertingmaterials. Another object of the present technology is to providecorresponding light-emitting elements coupled with light-convertingmaterials. In accordance with an aspect of the present technology, thereis provided a method for coupling one or more light-emitting elementswith a light-converting material, comprising providing a targetsubstrate, the target substrate associated with the one or morelight-emitting elements: providing a donor substrate proximate to thetarget substrate, the donor substrate comprising the light-convertingmaterial and configured to transfer a portion of the light-convertingmaterial to the target substrate upon a predetermined energization of acorresponding portion of the donor substrate; and controllablyenergizing one or more selected locations of the donor substrate,thereby transferring the light-converting material from the donorsubstrate to the target substrate at said one or more selectedlocations.

In accordance with another aspect of the present technology, there isprovided a lighting device comprising one or more light-emittingelements of a first size; and a pattern of light-converting material,the light-converting material operatively coupled to the light emittingelements, the pattern comprising one or more features having a secondsize smaller than the first size.

In accordance with another aspect of the present technology, there isprovided an apparatus for coupling one or more light-emitting elementswith a light-converting material, the apparatus comprising an operatingarea configured to receive a target substrate, the target substrateassociated with the one or more light-emitting elements; the operatingarea further configured to receive a donor substrate proximate to thetarget substrate, the donor substrate comprising the light-convertingmaterial, the donor substrate configured to transfer a portion of thelight-converting material to the target substrate upon a predeterminedenergization of a corresponding portion of the donor substrate; a lasersystem configured to energize one or more selected locations of thedonor substrate located in the operating area, thereby transferring thelight-converting material from the donor substrate to the targetsubstrate at said one or more selected locations; and a motion systemconfigured to align the laser system to aim laser light generatedthereby at the one or more selected locations.

BRIEF DESCRIPTION OF THE FIGURES

These and other features of the technology will become more apparent inthe following detailed description in which reference is made to theappended drawings.

FIG. 1 illustrates a method for coupling one or more light-emittingelements with a light-converting material, in accordance withembodiments of the present technology.

FIG. 2 illustrates aspects related to transferring a pattern oflight-converting material from a donor substrate to a target substrate,in accordance with embodiments of the present technology.

FIG. 3 illustrates an apparatus for coupling one or more light-emittingelements with a light-converting material, in accordance withembodiments of the present technology.

FIG. 4 illustrates a cross-sectional view of a target substratecomprising an encapsulant layer, in accordance with embodiments of thepresent technology.

FIG. 5 illustrates a top view of target substrate comprisinglight-emitting elements in a spaced-apart arrangement, in accordancewith embodiments of the present technology.

FIG. 6 illustrates a cross-sectional view of a transparent targetsubstrate separated by an air gap from associated light-emittingelements, in accordance with embodiments of the present technology.

FIGS. 7A and 7B illustrate, in cross section, aspects of a transferprocess provided in accordance with embodiments of the presenttechnology.

FIG. 8A illustrates a top view of a target substrate having alight-converting material applied in a substantially contiguous pattern,in accordance with embodiments of the present technology.

FIG. 8B illustrates a top view of a target substrate having alight-converting material applied in a ‘checkerboard’ pattern, inaccordance with embodiments of the present technology.

FIG. 8C illustrates a top view of a target substrate having alight-converting material applied in an irregular pattern, in accordancewith embodiments of the present technology.

FIG. 9 illustrates exemplary placement-tolerant patterns, in accordancewith embodiments of the present technology.

FIG. 10 illustrates exemplary placement-sensitive patterns, inaccordance with embodiments of the present technology.

FIG. 11A illustrates chromaticities that can be achieved using a singlelight-converting material applied to a target substrate, in accordancewith an embodiment of the present technology.

FIG. 11B illustrates chromaticities that can be achieved using twodifferent light-converting materials applied to a target substrate, inaccordance with an embodiment of the present technology.

FIGS. 12A to 12C illustrate target substrates applied withnon-overlapping or overlapping patterns of light-converting material, inaccordance with embodiments of the present technology.

FIG. 13A illustrates a typical prior art chromaticity-binning diagramused by a commercial LED manufacturer.

FIG. 13B displays a prior art chromaticity tolerance specification forgeneral illumination solid-state light sources.

FIG. 13C displays a hypothetical chromaticity distribution of a batch ofblue pump LEDs with white phosphor coating, produced in accordance witha prior art manufacturing process.

FIG. 13D illustrates a locus of achievable and tunable chromaticity's ofwhite light emitting phosphor coated blue LEDs manufactured inaccordance with an exemplary embodiment of the present, technology.

FIG. 14 illustrates a spectrum of light due to emission of alight-emitting element being partially converted by plural phosphors, inaccordance with an exemplary embodiment of the present technology.

FIG. 15 illustrates a respective top view and a perspective view of aweb-fed apparatus for coupling one or more light-emitting elements witha light-converting material, in accordance with embodiments of thepresent technology.

FIG. 16 illustrates emission spectra of light emitted from combinationsof light-emitting elements and light-converting materials.

DETAILED DESCRIPTION OF THE TECHNOLOGY Definitions

The term “light-converting material” is used to define materials whichabsorb photons according to a first spectral distribution and emitphotons according to a second spectral distribution. Light-convertingmaterial may, in some embodiments, be described as “color-convertingmaterial.” Light-converting materials may comprise photoluminescentsubstances, fluorescent substances, phosphors, quantum dots,semiconductor-based optical converters, or the like. Light-convertingmaterials may comprise rare-earth elements.

The term “light-emitting element” (LEE) is used to define any devicethat emits radiation in any region or combination of regions of theelectromagnetic spectrum for example, the visible region, infraredand/or ultraviolet region, when activated by applying a potentialdifference across it or passing a current through it, for example.Therefore a light-emitting element can have monochromatic,quasi-monochromatic, polychromatic or broadband spectral emissioncharacteristics. Examples of light-emitting elements includesemiconductor, organic, or polymer/polymeric light-emitting diodes,optically pumped phosphor coated light-emitting diodes, optically pumpednano-crystal light-emitting diodes or any other similar light-emittingdevices as would be readily understood by a worker skilled in the art.Furthermore, the term light-emitting element is used to define thespecific device that emits the radiation, for example a LED die, and canequally be used to define a combination of the specific device thatemits the radiation together with a housing or package within which thespecific device or devices are placed. Examples of light emittingelements include also lasers and more specifically semiconductor lasers,such as VCSEL (Vertical cavity surface emitting lasers) and edgeemitting lasers. Further examples may include superluminescent diodesand other superluminescent devices.

As used herein, the term “about” refers to a +/−10% variation from thenominal value. It is to be understood that such a variation is alwaysincluded in a given value provided herein, whether or not it isspecifically referred to.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe are to which this technology belongs.

According to aspects of the present technology, methods, and processesare provided for disposing one or more materials on one or more targetsubstrates. Depending on the embodiment, the combination of thematerials and target substrates may provide a predetermined functionrelative to, in combination with or without certain system components.Depending on the embodiment, target substrates may be different from thecertain system components or they may be the same. Depending on theembodiment, system components and/or target substrates may include orexclude LEEs, sensors, filters or other objects. Depending on theembodiment, target substrates may be associated in a certain manner withother system components, for example by a relative spatial orientation,distance or other operational association. The functions may includeelectrical, magnetic, mechanical, thermal, optical, chemical, acousticor other functions. Such functions may be based on correspondingproperties or combinations of functions and/or properties provided bythe materials, tile target substrates and/or the other systemcomponents. Optical properties may include wavelength conversion, suchas provided by wavelength-conversion materials, certain refractive indexmaterials including negative refractive index materials as provided bycertain metamaterials, or other optical properties, for example. Thesystem may comprise or be configured as a luminaire, sensor, catalyticconverter, battery, or other system, for example. It is understood thatas described herein and as the case may be, light-converting materialmay be complemented or replaced with one or more materials other thanlight-converting material.

As illustrated in FIG. 1, the method 100 comprises providing 110 atarget substrate associated with the one or more light-emittingelements. The target substrate may or may not comprise thelight-emitting elements. The target substrate may comprise alight-emitting element, packaged set of one or more light-emittingelements, transmissive material optically coupled to one or morelight-emitting elements, or the like, as described herein. The method100 further comprises providing 120 a donor substrate proximate to thetarget substrate. The donor substrate comprises the light-convertingmaterial, and is configured to transfer a portion of thelight-converting material to the target substrate upon a predeterminedenergization of a corresponding portion of the donor substrate.Appropriate donor substrates are described in more detail herein. Themethod 100 further comprises controllably energizing 130 one or moreselected locations of the donor substrate, thereby transferring thelight-converting material from the donor substrate to the targetsubstrate at said one or more selected locations, for example inaccordance with a predetermined pattern. In embodiments of the presenttechnology, the energization may be performed by a suitable source ofvisible or non-visible light such as from laser, charged or neutralparticles such as ions or other waves and/or particles, or othersuitable source of energy. Depending on the embodiment, such a sourcemay be configured to provide energy to one or more substantially focusedlocations or defined areas of the donor substrate. Depending on theembodiment, the distribution of light-converting material on the donorsubstrate may be substantially uniform, non-uniform or have apredetermined pattern in thickness and/or lateral extension parallel tothe donor substrate, for example. The transfer may be accomplished in awriting or masking manner as described herein.

The method 100 optionally comprises steps of evaluating 140 quality oflight from the one or more light-emitting elements associated with thetarget substrate, evaluating 150 properties of light-converting materialassociated with the donor substrate, and determining 160 an appropriatepattern based on the evaluations performed in steps 140 and 150. Steps140, 150, and 160 are optional in some embodiments of the presenttechnology. Evaluation 140 may comprise measuring chromaticity or thespectral power distribution or other quality of the light of thelight-emitting elements. Evaluation 150 may comprise measuringchromaticity or the spectral power distribution of light emitted by thelight-converting material when subjected to a predetermined input lightor other property of the light-converting material. Determining anappropriate pattern 160 may comprise determining an amount and surfacecoverage of the light-converting material to be applied to provide adesired chromaticity or spectral power distribution or other quality ofcombined light from the light-emitting elements and light-convertingmaterial, given their evaluated qualities.

Manufacturing methods and processes as described herein may beconfigured to provide predetermined control of the location and amountof disposition of light-converting material at or beyond a predeterminedhigh level, and can be employed to control light conversion and opticalpath formation within corresponding apparatuses in a predeterminedmanner. Depending on the embodiment, amounts of light-convertingmaterial may be employed that are smaller than those required byconventional manufacturing methods for the manufacture of apparatuseswith like properties that are based on like light-emitting elements, forexample. This may aid in conservation of rare earth elements, which inturn may limit manufacturing cost. For example, light-convertingmaterial on the order of just a fraction of a cubic mm may be needed perapparatus. Furthermore, processes as described herein can providepredetermined chromaticity tolerances and consequently can provide highmanufacturing yield in terms of ratio of devices that meet predeterminedcharacteristics versus all devices made by the process. Moreover, unuseddonor substrate can be reused, for example, it can be reground andblended back into new donor substrate. In comparison extraction of rareearth elements from conventional silicon-gel material is expensive. Assuch, the quantity of light-converting material and therefore thequantity of rare earth materials included therein may be reduced withsuitably configured processes as described herein. Depending on theembodiment, this may aid in the economical deposition of standard aswell as new and possibly expensive light-converting and/or othermaterials.

FIG. 2 illustrates aspects of transferring of a pattern 210 oflight-converting material from a donor substrate 220 to a targetsubstrate 250, in accordance with some embodiments of the presenttechnology. An exploded view of the donor substrate 220 is shown. Alaser or other energy carrying beam 205 as further described herein thatis incident on the donor substrate 220 controllably traces out thepattern 210 to be transferred. The pattern 210 may comprise discretepixels of predetermined size, which correspond to substrate locationssubjected to laser pulses of a predetermined pulse length and power.Depending on the embodiment, the pattern 210 may comprise asubstantially continuous pattern of features. The donor substrate 220comprises a transparent carrier substrate layer 225, a transfer layer235 comprising the light-converting material to be transferred, and arelease layer 230 between the carrier substrate layer 225 and thetransfer layer 235. The release layer absorbs energy from the laser beam205, and subsequently drives a localized transfer of light-convertingmaterial in the transfer layer 235 to the target substrate.

Another aspect of the present technology provides an apparatus forcoupling one or more light-emitting elements with a light-convertingmaterial. The apparatus comprises an operating area configured toreceive a target substrate, the target substrate associated with the oneor more light-emitting elements. The operating area is furtherconfigured to receive a donor substrate proximate to the targetsubstrate. The donor substrate comprises the light-converting materialand is configured to transfer a portion of the light-converting materialto the target substrate upon a predetermined energization of acorresponding portion of the donor substrate.

The apparatus further comprises a system of one or more lasers or othersuitable energy sources configured to energize one or more selectedlocations of the donor substrate located in the operating area. Theenergization initiates a physical and/or chemical reaction that causes atransfer of the light-converting material from the donor substrate tothe target substrate at said one or more selected locations. Thetransfer is typically substantially local to the energization location.The apparatus further comprises a motion system configured tocontrollably align light from the laser system with the one or moreselected locations for energization. The motion system may comprise asupport system and various mechanical actuators for controllablyproviding translational and/or rotational motion of the laser, theoperating area, the target substrate, the donor substrate, or acombination thereof. Depending on the embodiment, the apparatus may beconfigured to manipulate target substrates and/or donor substrates thatare configured in endless or batch configurations.

An example apparatus 300, as generally described above, is illustratedin FIG. 3. The apparatus 300 comprises an operating area 310 configuredto receive a target substrate 315 and a donor substrate 320 proximate tothe target substrate. The apparatus 300 further comprises a laser 330configured to energize the selected locations of the donor substrate 320located in the operating area 310. The apparatus 300 further comprises amotion system 340 configured to controllably align the laser 330. Asillustrated, the motion system 340 comprises two end support rods, acenter support rod which is, movably attached to the end support rodsvia a track, the laser 330 movably attached to the center support rodvia a track.

The laser 330 may be configured to provide one or more spots of light,each having a predetermined shape and size at the operating area 310.The motion system 340 may be configured to permit positioning of thelaser light relative to the target with predetermined precision orspatial resolution. Depending on the embodiment, the laser itself or thetarget may be moved by the motion system 340 to energize and transferthe desired pattern.

According to an embodiment, an example apparatus may be configured toprovide a linear array of pixels at which laser light may be directed.Such an apparatus may employ a Kodak Squarespot™ product havingapproximately 240 pixels in a linear configuration, or other lineararray, for example. Depending on the embodiment, the linear array may beconfigured to provide light across a portion or the entire width of atarget substrate or operating area. Such an embodiment may be employedin a web fed or other process. In some embodiments the laser may providea 2D array of pixels. The target substrate may be stepwise imaged,thereby stitching individual portions of patterns of light-convertingmaterial together. Depending on the embodiment, a corresponding motionsystem may be optional or configured to provide translation of thelinear array in only one direction, for example. Translation may beprovided along, perpendicular or in another direction relative to theelongate extension of the linear array.

Another exemplary apparatus 1500, as generally described above, isillustrated in FIG. 15, which shows a top view and perspective view ofthe apparatus 1500. The apparatus 1500 resembles a web-fed system,comprising or accepting a flexible target substrate 1510 wrapped aroundand fed between rollers of the apparatus 1500 such as roller 1515. Therollers operate to feed the target substrate through an operating area1520. The apparatus 1500 further comprises or accepts a flexible donorsubstrate 1525 wrapped around and fed between rollers 1527 and 1528 ofthe apparatus 1500. As illustrated, the donor substrate 1525 is fedthrough the operating area 1520 substantially perpendicularly to thetarget substrate 1510, although other configurations may also be used.The apparatus 1500 further comprises an array of lasers 1530. Dependingon the embodiment, the array of lasers 1530 may comprise one or morelasers, for example, a linear array of adjacent, non-targetable ortargetable lasers. Lasers of the array 1530 may be addressed andoperated to illuminate nearby portions of the operating area, thusenergizing the donor substrate therein. By positioning portions of thetarget substrate 1510 in the operating area 1520, providing anadequately undepleted portion of donor substrate 1525, and controllablyenergizing selected portions of the donor substrate 1525 by appropriatecontrol of the laser array 1530, the target substrate 1510 may bepatterned with light-converting material in a controllable manner. Theapparatus 1500 further comprises computing and control electronicsconfigured for this purpose.

According to some embodiments, the array 1530 comprises plural lasersspaced at predetermined distances so that targeted illumination of theoperating area at a desired resolution is achievable by selectivelyactivating the appropriate laser. Depending on the embodiment, energydeposition may be directed in one or more ways in order to provide apredetermined targeting resolution. For example, the array 1530 may beconfigured, to be movable as a whole, or one or more of the lasers ofthe array 1530 may be to translatable and/or rotatable, or optics may beemployed that can focus the laser beams in one or more predeterminedlocations.

The rollers 1527 and 1528 operate to feed the donor substrate 1525 intoand out of the operating area 1520, such that regions of the donorsubstrate 1525 which are substantially undepleted of light-convertingmaterial are presented to the lasers for energization. These regions,after being depleted by one or more laser energization cycles, are thenmoved by operation of the rollers 1527 and 1528 so that they are nolonger energized. This may comprise moving the depleted regions out ofthe operating area 1520 altogether, although some localized depletedregions may remain for a time in the operating area 1520 while adjacentundepleted regions are energized. In some embodiments, movement anddepletion of the donor substrate 1525 is akin to movement of atypewriter ribbon. Computer vision systems can be employed to update amapping of the undepleted regions so that a motion control system canmaximize the use of the donor substrate. Such updating may be performedin situ, continuously or at predetermined events, for example. In someembodiments, an algorithm may be used to track the locations of depletedregions of the donor substrate, and to position the donor substrate suchthat only undepleted regions of the donor substrate are energized. Alength of donor substrate may thus be used until it is depleted to apoint where it is no longer feasible for use. It may be feasible torecycle used donor substrate such that remaining light convertingmaterial is extracted for re-use.

Yet another aspect of the present technology provides a lighting deviceproduced by the above method and/or a lighting device produced by aprocess comprising application of the above method to materials of thedonor and target substrates. The lighting device may be a solid-statelighting device with associated light-converting material, aphosphor-coated LED or device comprising same, a module, a lamp, aluminaire, or the like.

Yet another aspect of the present technology provides a lighting devicecomprising one or more light-emitting elements of a certain size and apattern of light-converting material. The light-converting material isoperatively coupled to the light-emitting elements, for example byapplying the light-converting material directly to the light-emittingelements and/or to a transparent or translucent coating, casing,covering, or the like, which is associated with the light-emittingelements. In some embodiments, the light-converting material may beformed in a pattern directly on an LED die, LED wafer. LED package, orother substrate. In some embodiments, the light-converting material maybe formed on an optically transmissive layer, housing, encapsulant, orthe like, which is optically coupled to one or more light-emittingelements. The pattern comprises one or more features having a secondsize. The second size may be smaller, substantially equal or larger thanthe size of the light-emitting elements and/or an image of thelight-emitting elements, which may depend on the position of thefeatures relative to the light-emitting elements and/or the distancetherebetween. Depending on the embodiment, the pattern may be configuredto cover a predetermined portion of the surface to which it is applied,leaving a complementary portion free of the light-converting material.The pattern may be a discrete pixilated pattern or other pattern, andmay comprise a single layer of light-converting material such asphosphor, or plural layers of the same or different light-convertingmaterials. Pattern, features may relate, to pixels or groups of pixels,or other shapes of light-converting material. Each layer comprises apredetermined pattern of material, which is configured for example toprovide a desired chromaticity of combined light from the lightingdevice. The pattern or patterns of light-converting material, may beprovided by a method or process as described herein, or by anothermethod. In embodiments of the present technology, the pattern featuresmay be custom configured to the light-emitting element, for example tocover a predetermined surface area thereof, thus providing ability ofchromaticity tuning of combined light emitted by the right-emittingelement and light-converting material.

Embodiments of the present technology employ a thermal or non-thermaltransfer process, for example a laser-transfer or other process asdescribed herein. Depending on the embodiment, the transfer process maybe configured to make use of addressability, resolution and light outputpower of a suitably configured imaging or other system to transferappropriate amounts and types of light-converting and/or other materialfrom one or more donor substrates to a target substrate. The transferprocess may employ energy carrying beams of waves and/or particles suchas photons, phonons, electrons, ions or other particles with suitablekinetic energies and/or particle masses, or combinations thereof tocause a thermal, non-thermal, sputtering, ablative, electrostatic,ultrasonic, acoustic, detonative, piezoelectric and/or otherwisestimulated transfer of material from a donor substrate onto and/or intothe target substrate. Depending on the embodiment, the transfer processmay employ one energy-carrying beam or a combination of energy-carryingbeams. Combinations of energy-carrying beams may be employed to performa corresponding, material transfer in one or more stages. For example,one or more of the energy-carrying beams may facilitate an activation ofmaterial from the donor substrate, one or more of the energy-carryingbeams may be configured to facilitate a spatial transfer of the materialand/or one or more of the energy-carrying beams may facilitate an actualdisposition of material on the target substrate.

Embodiments of the present technology facilitate fine control overpatterning of light-converting materials onto target substrates. Forexample, in one embodiment, discrete ‘pixels’ of light-convertingmaterial may be reliably transferred to the target substrate using alaser, each pixel having a diameter or edge length of about 10 μm(micrometers). Assuming adjacent pixels of this size in a square grid, a1000 μm square area of target substrate can be patterned with 2^(10,000)different pixel patterns. A variety of pixel patterns, the design andlayout of which would be readily understood to those skilled in the artbased on the present, disclosure, may be used for patterning selectedportions of the area differently, for example to compensate forvariability of light intensity emitted by different portions of alight-emitting element or array. Furthermore, the proportion of targetsubstrate covered by light-converting material in this example can becontrollably varied from 0% to 100% in 0.01% increments, thus varyingcoverage from no application of light-converting material to completecoverage of the area. As such, the amount of light-converting materialapplied, and hence the resulting chromaticity of the coupledlight-emitting element and light-converting material can be finelycontrolled.

Patterns of light-converting material, such as pixellated patterns maycomprise one light converting material or overlapping, partiallyoverlapping, or non-overlapping regions of different light-convertingmaterials. Different portions of patterns may abut against each other orbe placed in a spaced-apart manner. Spacing between pattern portions maybe configured to allow a desired portion of substantially unconvertedlight from light-emitting elements to escape and mix with convertedlight to provide a desired chromaticity of mixed light. Spacing betweenpattern portions may or may not be present. Patterning may also refer topatterns of varying thickness of identical light-converting material.Pixels may be round, square, triangular, hexagonal, or otherwise shaped,and may be patterned in close proximity to form pattern features ofsubstantially arbitrary shape. A regular or irregular tiling of thetarget substrate may be utilized, with each pixel occupying all or aportion of each tiling element. In some embodiments, overlappingpatterns of light-converting material may be used to create gradationsin the amount of light converted. A three-dimensional pattern oflight-converting material may thus be formed. For example, portions ofthe pattern corresponding to relatively thinner layers oflight-converting material may convert less light than portions of thepattern corresponding to relatively thicker layers, thus varyingchromaticity. In embodiments comprising plural light-convertingmaterials, the pattern may be configured to control or limitcannibalization between different light-converting materials.Cannibalization comprises unwanted loss of already converted light insubsequent layers of light-converting material, including absorptionand/or conversion at lower quantum efficiencies in subsequent layers,for example.

More generally, for a target substrate having area A square units and aresolution of donor substrate locations of ‘pixels’ per square unit, atotal of 2^(p)*^(d) different pixel patterns are possible. Pixels may bearranged in a square grid, or in another pattern such as a hexagonalgrid or irregular arrangement. Pixels may be square, circular, regularlyshaped and sized, stochastically screened or irregularly shaped andsized. In some embodiments, substantially continuous patterns oflight-converting material may be applied to the target substrate ratherthan discrete pixels. In this case, the concept of ‘pixel’ may bereplaced by or be associated with the concept of minimum achievablefeature size of the pattern.

In some embodiments, multiple layers of light-converting material suchas phosphors may be applied to a target substrate in an ‘overwriting’process. In this process, plural patterned layers of the same type ordifferent types of light-converting material are applied in overlappingor non-overlapping layers to the target substrate. Each patterned layermay be applied sequentially. This provides an additional level ofcontrol over the amount, pattern and combination of light-convertingmaterial applied, thereby facilitating fine control or tune-ability ofthe resulting chromaticity of the coupled light-emitting element andlight-converting material or materials.

Embodiments of the present technology may optionally comprise,pre-evaluation, of one or both of the light-emitting elements and thelight-converting material, and adjustment of the coupling, for exampleadjustment of the light-converting material pattern, based on thepre-evaluation.

In some embodiments, light-converting material may be applied in apredetermined three-dimensional pattern to a three-dimensional surfaceof the target substrate. This may be useful to facilitate conversion oflight emitted by different types of LEEs as explained herein. Forexample, such three-dimensional surfaces may include one or morelight-emitting surfaces of light-emitting elements and may depend on thetype of light-emitting element. Depending on the embodiment, theduration and power of laser or other pulses may be adjusted to achieve apredetermined coating around edges of a light-emitting element, forexample.

Types of light-emitting elements may include horizontal, vertical,flipchip or other forms of LEDs, for example. In an examplemanufacturing process, an epitaxial layer is grown on a sapphiresubstrate. In this example, the epitaxial layer may be about 3 to 10microns thick and includes a buffer layer to accommodate thermalexpansion and lattice mismatch between the sapphire substrate and theGaN LED structure, which is disposed over top thereof and comprises an-GaN layer, the active light emitting region and a p-GaN layer. Thethickness of the LED die may be about 70 to 250 microns. According toanother example for a horizontal LED, an LED mesa is formed on thesapphire substrate and both p and n contacts are formed on the topsurface. Light generated in the active region escapes from the LED diethrough all surfaces.

According to another example for a vertical LED die, the epitaxial layeris removed from the sapphire substrate and bonded to an electrically andthermally conductive substrate. During this process a mirror layer maybe incorporated between the new substrate and the epitaxial layer thatoptically separates the substrate from the active region. One electricalcontact is formed on the top and one on the bottom substrate. Dependingon the embodiment, the n-contact may be located on the top of the LEDdie. In this example, light emission substantially occurs through thetop surface. Consequently, light-converting material may be disposedand/or concentrated substantially proximate the top light-emittingsurface. According to another example for a flip chip LED, both n and pcontacts are formed on the top surface and, subsequently, the LED die isflipped and bonded to a target substrate with matching electricalpattern. Optionally, the sapphire substrate may be removed. A flip chipmay be configured to provide both electrical contacts on the bottom ofthe die leaving the entire top surface accessible for placement ofoptics or deposition of phosphors.

Depending on the embodiment, patterning of light-converting material maybe varied across the target substrate to compensate for spatialvariability in light emitted by light-emitting elements. Such spatialvariability may arise from adjacent or proximate opaque elements such asoperative contacts, bonds, metallization patterns or other elementsassociated with a light-emitting element. Furthermore, shadowing due tometallization contact patterns and variation of light generation acrossthe die may be due to non-uniform carrier densities due to electron andhole injection variation, into optically active regions, which cantranslate into non uniformity in the photon generation in the activeregion and variation of the brightness across an LED die, which can leadto an intricate brightness variation across the surface of the LED die,for example. Different amounts and/or types of light-convertingmaterials may be patterned in different regions to at least partiallycompensate for such spatial variability and achieve greater uniformityof the light emission.

Consequently, light-converting material may be applied in apredetermined three-dimensional pattern to a three-dimensional surfaceof the target substrate, such as a generally flat substrate withpredetermined relief. For example, when the target substrate consists ofor comprises a light-emitting element, such as a horizontal LED, whichexhibits a significant amount of light emission through facets on theside of the light-emitting element, it may be desirable to achievetransfer of the light-converting material not only to the lop surface ofthe light emitting element, but also to the sides of the light emittingelement.

In some embodiments, three-dimensional patterning, such as patterning ofside facets of a light-emitting element, may be performed in a number ofways. For example, an area of light-converting material larger than thearea of the LED die top surface may be released from the donorsubstrate, transferred to the die target surface and moulded around thetarget surface including the sides of the LED die via at least, partialliquefaction. Light-converting material may be released from the donorsubstrate by melting, evaporation, sublimation, sputtering or otherprocess. Light-converting material may be disposed on the target,substrate via solidification, condensation, implantation and/or otherprocess, for example. Depending on the embodiment, an oversized area oflight converting material may be energised and evaporated so that acloud of light-converting, material is created which wraps around thethree-dimensional features and condenses on both the top and sidesurfaces of the LED die.

In some embodiments, sides of light-emitting elements may be coated withlight converting material by aiming and projecting light-convertingmaterial at an angle at the light-emitting element. The plane of thetarget substrate or the laser may by tilted substantially away from anaxis perpendicular to the top surface of the light-emitting element, sothat light-converting material arrives on a corresponding, side surfacesubstantially to generate a corresponding coating.

Depending on the embodiment, one or more of the target substrate, donorsubstrate, and sources of energy such as lasers for energizing the donorsubstrate, may be controllably oriented, so that the donor material canbe applied to the target substrate at angles that provide normal orclose to normal incidence with respect to the target substrate at thatlocation. Depending on the embodiment, three-dimensional targetsubstrates may be effectively patterned, since greater resolution and/orefficacy can be achieved by applying the light-converting material at asubstantially perpendicular angle to the target substrate, inembodiments of the present technology.

Target Substrate

Embodiments of the present technology comprise or relate to a targetsubstrate, which is associated with one or more light-emitting elements,and to which light-converting material is applied, for example in one ormore layered patterns. The target substrate may comprise or be opticallycoupled with a single light-emitting element or plural light-emittingelements. Thus, for example, the target substrate may comprise a set ofone or more light-emitting elements, an LED wafer, a planar surface suchas a circuit board comprising light-emitting elements thereon, apackaged light-emitting element, a surface comprising light-emittingelements and one or more optically transmissive materials thereon, suchas encapsulation layers, an optically transmissive material opticallycoupled but spaced apart from one or more light-emitting elements, oneor more optical components of a system that may be proximate ordisplaced from the LEEs, or the like. Generally, light-convertingmaterial is patterned and/or deposited on a target substrate, andwherein the target substrate receives, conveys, and/or generates lightto be transmitted to the patterned light-converting material.

In embodiments of the present technology, the target substrate comprisesthe one or more light-emitting elements. The target substrate may be anLED wafer, a collection of LEDs (for example from a diced wafer) mountedon a tape, a chip-on-board arrangement of light-emitting elements, apackage comprising a single light-emitting element or plurallight-emitting elements, an LED package, an LED die, a closely packedarray of singulated light-emitting elements such as LED dies on acarrier substrate, a diluted array of singulated light emitting elementssuch as LED die on a carrier substrate, a light-emitting elementcomprising a light-converting material applied by another method, or thelike. LEDs may be horizontal, vertical, flip-chip, or other types ofLEDs. The target substrate may also be or comprise a semiconductor laserwafer, a collection of lasers such as VCSELs on tape, densely or dilutedpacked on a carrier substrate.

In some embodiments, the target substrate comprises one or morelight-emitting elements and further comprises an optically transmissiveencapsulant formed over the light-emitting elements. The encapsulant mayprovide physical protection to the light-emitting elements. Theencapsulant may be configured as a suitable surface for receiving andretaining the light-converting material. The encapsulant may provide athermal barrier between the light-emitting elements and thelight-converting material to inhibit breakdown of the latter. Theencapsulant may be configured to diffuse and/or filter light from thelight-emitting elements. The encapsulant may facilitate planarization ofthe target substrate. In one embodiment an LED die comprising a profileof protrusions and recesses may be covered by an encapsulant having, acomplementarily varying thickness, thus providing a substantially planarsurface to the target substrate. In a different embodiment theplanarization layer creates a localized plane surface around one of aplurality of light emitting elements, thereby facilitating the transferof color converting material over an area larger than the individuatedlight emitting element. The encapsulant may function as a diffusionbarrier to protect an LED die from material incorporated in thelight-converting material.

FIG. 4 illustrates a cross-sectional view of a target substrate 410comprising light-emitting elements 412, 414, such as LEDs and anencapsulant layer 420. Patterns of light-converting material 430, 440are disposed on the encapsulant layer 420. As illustrated, the patterns430, 440 may be positioned overtop of the light-emitting elements 412,414. As also illustrated, the patterns 430, 440 may be oversizedrelative to the light-emitting elements 412, 414, for example such thatportions of the pattern 430 extend a distance 435 beyond the edge of thelight-emitting element 412.

In some embodiments, a surface of the target substrate is configured toincrease receptivity of the light-converting material. For example, thesurface may be plasma etched or otherwise textured, or roughened, toincrease tackiness, or an adhesive such as silicone or B-staged siliconemay be layered on the surface.

In some embodiments, the target substrate may comprise plurallight-emitting elements adjacent or in close proximity to each other. Insome embodiments, the target substrate, with or without an encapsulantsuch as a diffusing and/or planarizing encapsulant, may comprise plurallight-emitting elements in a spaced-apart or diluted arrangement, thelight-emitting elements thereby covering a predetermined fraction of thetarget substrate. The light-emitting elements may be integrated andinterconnected on a carrier. For example, light-emitting elements may bespaced several millimeters from each other, and/or may be spaced apartin a regular or irregular pattern. Arrays of such configuration may beused for backlighting or general illumination, for example. FIG. 5illustrates a top view of target substrate 500 comprising light-emittingelements 510 in a spaced-apart arrangement.

In some embodiments, the target substrate comprises an opticallytransmissive material that is to be registered, at a later time, withone or more light-emitting elements. For example, the target substratemay comprise a sheet of manufactured glass, a transparent thermoplasticsuch as Polymethylmethacrylate (PMMA), polycarbonate, PET, ULTEM(Polyetherimide), combinations of layers, or other suitable material.The target substrate may overlay an additional substrate carrying lightsources, for example an array of phosphor coated or non-phosphor coatedLEDs. In some embodiments, the target substrate may be placed at apredetermined distance from the additional substrate, the two substratesbeing separated by an air gap, for example. FIG. 6 illustrates across-sectional view of transparent target substrate 600 comprising apattern of light-converting material 610 thereon, and associated withlight-emitting elements 620, 625 on another substrate 630. An air gap640 separates the target substrate 600 from the other substrate 630comprising the light-emitting elements 620, 625. A transparent ortranslucent encapsulant 645 may also be formed over the light-emittingelements. The target substrate and the light-emitting elements may besubstantially precisely aligned within a predetermined tolerance.

In some embodiments, the target substrate comprises one or more flipchip LEDs. In a flip chip LED the optical emission occurs through thetop surface, while electrical interconnects are provided on the oppositesurface of the LED. Such a topology can enable up to the entire topsurface of a flip chip LED to be covered with light-converting materialdepending on the embodiment.

In some embodiments, the target substrate comprises one or more verticalLEDs. In this case, the LED surface area to which light-convertingmaterial may be applied is reduced by the area required to provideelectrical connection to the vertical LED through wirebonding or otherprocess known to a person skilled in the art.

In embodiments of the present technology, LEDs may be LED dies such ashorizontal, vertical or flip chip LED dies, LED packages, chip on boardLEDs, or the like.

Donor Substrate

Embodiments of the present, technology comprise or relate to a donorsubstrate configured to transfer a portion of a light-converting orother material to the target substrate upon a predeterminedenergization. The donor substrate may be placed in contact with,proximate or distal of the target substrate and stimulated via a laseror other source as described herein in a predetermined pattern. Thosesites on the donor substrate that are adequately stimulated may react bytransferring light-converting material, held in the donor substrate, tothe target substrate.

According to some embodiments, the donor substrate may be placed overtop of the target substrate as a contiguous layer. A template may beplaced overtop of the donor substrate, or between the donor substrateand target substrate, the template having apertures defining generalregions where the transfer of light-converting material is to occur. Thetemplate and/or donor substrate may be mechanically separate,substantially flat substrates, or they may be temporarily bonded onto ordisposed, via a suitable mechanism, proximate or distal of the targetsubstrate, for example in accordance with lithographic techniques aswould be readily understood by a worker skilled in the art.

In some embodiments the donor substrate is comprised of plural layers,including a carrier substrate layer, a transfer layer, and a releaselayer, as described below. The transfer layer is located nearest to, forexample adjacent to, the target substrate, while the release layer islocated between the carrier substrate layer and the transfer layer. Insome embodiments, a single integrated layer may function as both thetransfer layer and the release layer. For example, materials of thetransfer layer and release layer may be substantially intermixed. Theintegrated layer may operate similarly to that described herein withrespect to separate transfer and release layers.

The carrier substrate layer may be formed of a material that is inert tothe transfer process, for example by virtue of transparency to the laseror other light-energy source. For example, the carrier substrate maycomprise glass, polyethylene terephthalate (PET), polymethylmethacrylate(PMMA), or the like. In some embodiments, the carrier substrate layermay comprise an antireflection coating, so that incident laser light isnot substantially reflected when it strikes the carrier substrate layer.

The transfer layer comprises one or more light-converting or othermaterials or precursor materials thereof. The transfer layer may includelight-converting material only or may comprise light-converting materialsuspended in another material such as a silicone elastomer. The transferlayer may comprise plural light-converting materials, in some,embodiments, plural light-converting materials may be mixed together. Insome embodiments, different light-converting materials may be confinedto different regions of the transfer layer, or be present in differentconcentrations in different regions.

According to some embodiments, the transfer layer comprises a B-stagedsilicone. The B-staged silicone layer may provide a partially curedlayer, which may be configured to re flow upon thermal actuation, forexample, by a laser. The layer may thus behave as a thermoplastic layer,in this way, the silicone is earned to the target substrate, for exampleLEDs thereof, in a partially cured and plastic state. The partiallycured silicone layer may then be further or fully cured by a subsequentprocess step to achieve a predetermined degree of polymerization.

In some embodiments, the transfer layer comprises the light-convertingmaterial along with a binder material, such as B-staged silicone (toconfer tackiness to the transferred silicone), a diffuser material suchas silica, fumed silica, finely divided glass particles, or AluminumOxide Al₂O₃, or a combination thereof. Depending on the embodiment, thetransfer layer may include thixotropic control materials such as fumedsilica, which can help maintain light-conversion material in suspensionduring the transfer process and control coagulation. In someembodiments, the binder material may aid in binding the light-convertingmaterial with the target substrate. In some embodiments, the bindermaterial aids in binding the light-converting material with the donorsubstrate until sufficient energization. The diffuser material may actas a scattering center, thereby aiding blending and mixing of theemitted light by increasing the path length of the rays within thelayer.

The release layer is configured to initiate transfer of thelight-converting material to the target substrate upon energization, forexample via a laser light source. Generally, the release layer isconfigured to physically and/or chemically drive direct transfer oflight-converting material to the target substrate when energized locallyby a suitable energy source. The release layer may undergo a chemicalreaction, a physical state change, a change in temperature, or the like,or a combination thereof. In some embodiments, referred to herein as athermally-activated process, the release layer may be configured toconvert energy due to the energization into heat. The heat may then beused to drive the transfer of light-converting material to the targetsubstrate. In some embodiments, referred to herein as a photon-activatedprocess, the release layer may be configured to decompose uponenergization, for example due to a UV laser.

In some embodiments related to the thermally-activated process, therelease layer may comprise an absorbing material such as a continuouslayer of metal oxide, black aluminum, or other suitable material thatconverts electromagnetic energy in a predetermined spectrum to heat. Theabsorbing material may be embedded as a powder within the release layeror coated onto the carrier substrate, for example.

In some embodiments related to the thermally-activated process, therelease layer may comprise material that is capable of nitrogenproduction at a temperature, such as an organic azide. This material maybe applied as a continuous layer or as intermixed with a heat absorbingmaterial. Upon energization via an IR laser beam, the heat absorbingmaterial converts the light into heat, which stimulates localizednitrogen gas production by decomposition of the organic azide. Theproduced gas causes an expansion, which propels a correspondinglocalized portion of light-converting material toward the targetsubstrate.

In some embodiments related to the thermally-activated process, therelease layer comprises an absorbing material, and the transfer layercomprises the light-converting material along with a binder materialthat is configured to liquefy at a predetermined temperature. Suchbinder materials may include B-staged silicones, PET, PMMA,Poly-m-methoxytoluene (PMMT), Polyester, Polycarbonate, polyolefins,Polyamide, or other materials. Upon energization, the materials in thetransfer layer will liquefy, thereby facilitating transfer of thelight-converting material to the target substrate. The target substratemay be configured to bind to the liquefied materials, or to receive themunder diffusion, gravity, electrostatic attraction, bonding to activatedsurface states or the like.

In some embodiments related to a photon-activated process, chemicalbonds in materials, such as materials in the donor substrate releaselayer, are broken due to the photon energy rather than thermal effects.Such materials in the release layer may thereby be configured todecompose upon irradiation with near UV light. Once bonds in the releaselayer are broken, the light-converting material in the transfer layermay tend to be attracted to the target substrate. Attraction may be dueto effects such as gravity, chemical attraction, electrostaticattraction, adhesive binding, or the like. In some embodiments, anorganic azide can be induced to decompose by photon energy or thermalenergy.

As will be readily understood, the donor substrate is typicallyconfigured so that transfer of light-converting material issubstantially local to a predetermined energization. For example, alaser beam incident on a first, region of the donor substrate may drivetransfer of light-converting material contained in the first region,possibly along with light-converting material in a second regionsurrounding the first region. The second region may be controllablylimited in its cross-sectional area, thereby improving resolution of thetransfer process.

In an exemplary embodiment, the transfer layer comprises a polymericmaterial containing light-converting material in the form of phosphorparticles having mean particle diameters of between 3 μm and 10 μm.Other diameters may also be used. The weight percent of light-convertingmaterial such as phosphor particles in the donor substrate may be ofvarious amounts, limited at the upper end for example by the ability ofthe polymer substrate to retain its shape and/or integrity. Sufficientbinder material should be present to retain integrity of the substrate.The polymeric layer may be a silicone rubber sheet, which is of opticalquality transparency. More specifically a B-staged silicone rubber sheetmay be used, which is not fully cured, as would be readily understood bya worker skilled in the art. The purpose of the B-staging of thesilicone is to confer thermoplastic, and tackiness properties to thetransferred silicone drops. If the silicone is not B-staged, thesilicone can behave as a thermoset material, limiting the case ofcoating the light emitting elements. In some embodiment, the sheetthickness may be between 30 microns and 1 mm. In some embodiments, thesheet thickness is on the order of the pixel size of the pattern oflight-converting material. In some embodiments, the sheet thickness isselected so that thermally-induced transfer of light-converting materialcan be adequately carried out using an energy source, such as a laser,of a given power. The sheet is laminated onto a carrier substrate layerof glass, PET, PMMA, Polyester, Polycarbonate or other substrate. Insome embodiments a layer of absorbing material such as metal oxides maybe placed between the carrier substrate and the sheet. Upon laserenergization the transfer layer is liquefied and subsequently at least aportion thereof is transferred to the target substrate.

In some embodiments, the donor material may include a composition ofparticles of light-converting material and additional materials such astransparent glass particles in dimensions and densities that provideadjustable spacing between light-converting material particles. Suitableglass particles can be made in a variety of sizes and shapes that can beemployed in industrial processes. If the glass particles andlight-converting material particles are heated such that the glassparticles begin to soften and flow then it may be optionally possible tofuse the materials together within a composite structure with usefulmechanical and optical properties. This structure may be controlled interms of spacing of the constituent particles such that the ratio ofdistances between light-converting material particles and theintervening free space for propagation of light is balanced to provide apredetermined utilization of light-converting materials and for example,maximize the overall optical throughput through the resulting materialmatrix. If the composite material is then placed on a carrier layer andthe release layer is energized, then the efficacy of removal oflight-converting material may be improved as the glass bonds may bebroken preferentially through energization within a boundary of a regionwhich creates a substantially homogenous section of compositelight-converting material to be released to the target substrate.

In some embodiments, the glass particles may be primarily located onone, or both, of the top and bottom surfaces of the light-convertingmaterial layer. If the glass particles are fused together then they canbe used to create a protective layer on one, or both sides of thelight-converting layer. At an appropriate temperature, the glassparticles can be softened and flow together and slightly into thelight-converting material. This layer will also create a mechanicalassociation to many light-converting material particles such that theycan retain their consistency after the release layer is energized andalso provide a degree of protection to the light-converting materialparticles.

According to some embodiments, the donor substrate can optionally bemade of glass where the light-converting particles are heated andallowed to be adhered to the surface to some depth. This provides aconvenient mechanical substrate and protective barrier. If thissubstrate is chemically or mechanically scored with a fine pattern ofcleave lines then this may enable a convenient removal via energizationof a release layer of a platelet of light-converting material. Theoverall stack structure presented to the target substrate would be abonding layer over the light-converting layer which in turn is incontact with the thin glass layer that is adhered to the targetsubstrate. Optionally, the glass donor substrate could be patterned withpredetermined relief structures such as lenses or other optically activesurfaces to re-direct or enhance light emission profiles.

In some embodiments, when the light-emitting elements of the targetsubstrate emit high-intensify, short-wavelength blue light, the use ofsilicone or silicone-based polymers is preferred, insofar as suchpolymers are resistant to decomposition under this type of light.

Transfer Process

In embodiments of the present technology, one or more light-convertingor other materials, each having its own predetermined characteristics.Such as photoluminescent characteristics giving rise to a predeterminedchromaticity, are transferred from a donor substrate onto a targetsubstrate via a suitable transfer process. Embodiments of the presenttechnology may employ a thermal or non-thermal transfer process, forexample a laser-transfer or other process as described herein. Dependingon the embodiment, the transfer process may be configured to make use ofaddressability, resolution and light output power of a suitablyconfigured imaging or other system to transfer appropriate amounts andtypes of light-converting and/or other material from one or more donorsubstrates to a target substrate. The transfer process may employ wavesand/or particles such as photons, phonons, electrons, ions or otherwaves and/or particles with suitable kinetic energies, or combinationsthereof to cause a thermal, non-thermal, sputtering, ablative,electrostatic, ultrasonic, acoustic, detonative, piezoelectricallyactuated, and/or otherwise stimulated transfer of material from a donorsubstrate onto and/or into the target substrate.

Depending on the embodiment, the transfer process may be performed byexposing predetermined small or large portions of donor substrate to oneor more beams of suitable waves and/or particles as described herein.One or more beams may be configured with a width small enough totransfer a pattern in a sequential manner, which may also be referred toas writing. Or one or more beams may be wide enough to expose largeportions of the donor substrate in combination with a suitablyconfigured mask that is adequately disposed relative to the donorsubstrate and the target substrate, or a pre-structured donor substrateto transfer at least large portions of a pattern in a substantiallysimultaneous fashion, which may also be referred to as masking.

A laser or otherwise induced transfer process may utilize varioustechniques that would be readily understood by a worker skilled in theart. Those techniques include but are not limited to ablative processes,melt stick processes or a Xerographic or electrostatic process. In anablative process, a material absorbs energy at the wavelength of anincident laser or other light-energy source. The energy may be convertedinto heat and result in ablation of a material, such as a material inthe release layer. The ablation may remove binder material in the donorsubstrate through chemical decomposition and/or destructive charring ofthe donor substrate, allowing the light-converting material to insteadbind to the target substrate. A melt stick process refers to a processwhereby a thermoplastic substrate is raised above its melting point andmelted droplets are removed from the donor substrate.

In an exemplary Xerographic or electrostatic process, a laser is used toremove previously deposited electrostatic charges from portions of acarrier substrate. The charges may be removed in a latent pattern or ina negative of the latent pattern. Powdered material containing thelight-converting material, optionally associated with electrostaticallyactive particles, is introduced and attracted to the carrier substratein the desired pattern. The target substrate is then brought intoproximity with the carrier substrate, and the patterned light-convertingmaterial is transferred to the target substrate. Subsequent steps may beperformed to more permanently affix the light-converting material to thetarget substrate. Such processes, their steps, and their variants aregenerally understood in the art and are not described in further detailhere. In some embodiments of the Xerographic process, a powder, whichcomprises a sublimable or meltable material such as PVC along withlight-converting material, is sublimed or melted on to the targetsubstrate. Also for Xerographic processes, the light-converting materialparticles must be adequately responsive to electrostatic manipulation.Since most known phosphors are relatively dense, this may pose achallenge unless a large amount of charge is used. Otherlight-converting materials such as quantum dots may be less dense andthus more amenable to electrostatic manipulation.

In some embodiments of a Xerographic process, light-converting materialis electrostatically attracted to a rotating drum, where the locationsof attraction are defined by a laser, through prior laser-based removalor deposition of charges to the drum. The resulting pattern oflight-converting material on the drum is then transferred to atransparent sheet, which is the target substrate. This may be done foreach light-converting material “color” just like for standard colorprinting. The light-converting material is then fixed, such as by curinga binder on the transparent sheet, and the sheet is then laminated overone or more light-emitting elements.

In some embodiments, the transfer can be facilitated using a thinrelease layer that contains nitrogen. The laser heat activates thenitrogen and propels particles of light-converting material away fromthe release layer. The receiving surface may then have a thin siliconelayer sprayed over it to retain the phosphor in place.

FIGS. 7A and 7B illustrate, in cross section, a transfer process inaccordance with an embodiment of the present technology. A targetsubstrate 710 is provided comprising plural light-emitting elements suchas LED 714 on a substrate 712. A donor substrate 720 is placed incontact with the target substrate 710 such that a transfer layer 726 ofthe donor substrate 720, comprising light-converting material, isadjacent to the target substrate 710. The donor substrate 720 furthercomprises a release layer 724 and a carrier substrate layer 722. Ahigh-resolution imaging head 730, such as ah ultraviolet or infraredlaser mounted to a movable platform, is used to irradiate portions ofthe release layer 724, such as portion 728. Irradiation of the releaselayer 724 drives a transfer of light-converting material from thetransfer layer 726 to the target substrate 710. Specifically,light-converting material is transferred locally at the irradiatedportions, such a portion 728, resulting in a pattern 738 oflight-converting material being transferred. The pattern may beadjusted, for example to cover a controllable portion of the targetsubstrate, thereby adjusting combined light emitted by thelight-emitting elements and light-converting material.

Pre-Evaluation

Some embodiments of the present technology comprise pre-evaluation ofone or both of the light-emitting elements and the light-convertingmaterial and/or other material, and adjustment of aspects of thecoupling between them based, on the pre-evaluation. Sets oflight-emitting elements and/or batches of light-converting material, forexample associated with sheets of donor substrate, may be pre-evaluatedby directly or indirectly measuring characteristics such as chromaticityor other optical properties. Based on this, an appropriate pattern,surface coverage and/or thickness of light-converting material,optionally along with selection of one or more appropriatelight-converting materials or particular sheets of donor substrate maybe selected, for example via a lookup table operation or via algorithm.The pattern may be selected based on the proportion of the targetsubstrate covered by said pattern. Thus, for example, the pixel densityor amount of patterned light-converting material can be adjusted tocompensate for chromaticity variation in the light-emitting elements,light-converting material, or both. An adequately high-resolutionpatterning process may be used to adequately finely tune thechromaticity of the combined light-emitting elements andlight-converting materials. For example, the amount of surface areacovered by the pattern may be adjustable pixel-by-pixel, where eachpixel covers an area of 10 μm by 10 μm. Depending on the embodiment,pre-evaluation may provide for efficient utilization of light-convertingand/or other material.

In some embodiments, each light-emitting element, such as each LED waferor LED die, can be evaluated with respect to chromaticity or otherrelevant variable. Evaluation may be performed according to currentevaluation procedures known in the art, for example related to LEDbinning in bulk manufacturing processes. An algorithm may be used todetermine an appropriate type, amount and pattern of light-convertingmaterial to be applied to the light-emitting element to achieve achromaticity target. Furthermore, the properties of the light-convertingmaterial or materials and the interaction of these in proximity to theLED die may be measured, characterized, and factored into an algorithmor means to select the quantity and type of material to be applied toachieve a target chromaticity.

In some embodiments, each light-emitting element may be evaluatedindividually and an appropriate type and pattern of light-convertingmaterial may be applied based at least in part on said evaluation.

In some embodiments, properties of one or more representative andstatistically relevant samples of light-emitting elements from a group,such as a manufacturing batch, wafer or batch of wafers, may beevaluated. Such properties may include chromaticity or other propertiesof the light-emitting elements. Properties of other batches or wafersthat have not been evaluated may then be predicted within certaintolerance levels. Such a prediction may be based on statistics, takeinto account performance patterns based on the manufacturing equipmentand processes and/or other aspects, for example. Performance patternsmay be used for evaluating samples of sections of wafers or entire LEDwafers, for example. An appropriate type and pattern of light-convertingmaterial may be applied based at least in part on said evaluation.

In one embodiment, a sample of light-converting material may beevaluated by applying it one or more test patterns to a target substrateassociated with a light-emitting element with known characteristics,such as chromaticity. The output of combined light may be analyzed todetermine the properties of the sample of light-converting material.Light-converting material from the batch may be applied in appropriatepatterns based at least in part on said evaluation.

In some embodiments, where possible, quantities of light-convertingmaterial, such as associated with a specific donor substrate, may beevaluated individually to determine properties such as chromaticity, anda pattern in which that quantity of light-converting material is appliedmay be based at least in part on said evaluation.

For example, an algorithm may receive as inputs the measuredchromaticity of a light-emitting element and a desired chromaticity ofthe combined light-emitting element and light-converting materialapplied thereto. The algorithm may further receive as input theavailability and characteristics of one or more available donorsubstrates, for example related to the type of light-convertingmaterials of each substrate and/or evaluated characteristics of same.The algorithm may calculate a patterning solution or perform a tablelookup to determine a patterning solution. The patterning solution mayinclude one or more particular donor substrates and/or particularlight-converting materials to apply to the target substrate. Thepatterning solution may include a specification of patterns in whichspecified light-converting materials are to be applied to the targetsubstrate, and/or a specification of proportions of the target substratewhich are to be covered by specified light-converting materials. Thepatterning solution may include a specification of patterns of plurallayers of light-converting materials to be applied to the targetsubstrate. Plural layers may comprise similar or differentlight-converting materials in overlapping or non-overlapping patterns.

In some embodiments, the algorithm may be adjusted in real-time basedupon process parameters acquired in situ to further fine tune theapplication of material. As patterns are applied in the process,in-process testing may be used to measure changes in the outputparameters and provide, feedback into the process that adjusts theprocess to avoid any drift in quality.

As described above, pre-measurement and subsequent adjustment oflight-converting material selection and patterning based thereon canfacilitate manufacturing of products having more precise and/orconsistent characteristics, such as chromaticity. This may be used tocompensate for variabilities in sourced light-emitting elements to bepatterned, as well as sourced light-converting materials. The highresolution with which the patterns of light-converting material can beadjusted allows for production of a highly consistent product even whensourced materials are relatively inconsistent. In some embodiments,single or multiple rounds of feedback can be implemented. In each round,the product is evaluated and an appropriate light-converting materialand/or pattern is determined for bringing the product closer to adesired set of characteristics of emitted light.

Substrate Registration

In embodiments of the present technology, the target substrate isregistered with respect to its presence, position and/or alignmentrelative to an energization source such as a laser. This facilitatesaccurate patterning of light-converting material onto the targetsubstrate. A position of the target substrate may be measured relativeto a baseline coordinate system, so that physical offsets between thetarget substrate and the baseline coordinate system may be compensatedfor, thereby reducing potential for pattern misalignment and henceimproving accuracy of chromaticity or other aspect of the resultingproduct. Registration may be performed via an optical system such as amachine vision system, via mechanical sensors, or a combination thereof.

Pattern Selection

In embodiments of the present technology, the pattern is configured tocover a portion of the target substrate commensurate with a desiredchromaticity. As will be readily understood, the chromaticity of lightresulting from the combined operation of light-emitting elements andlight-converting material depends in part on the proportion of targetsubstrate covered by light-converting material. For example, for atarget substrate associated with a blue LED light-emitting element,increasing the area of the target substrate occupied by yellow phosphor(which luminesces in the presence of the blue LED) will adjust theresultant combined chromaticity toward that of the yellow phosphor andaway from that of the blue LED. Each incremental increase in area ofyellow phosphor will adjust the chromaticity by a correspondingincremental amount. In some embodiments, the pattern is configured basedon measured or anticipated spatial variation in light emitted by thelight-emitting elements. The pattern may thereby be configured tocompensate for chromaticity and/or luminance variations related to thetarget substrate, thereby providing a more uniform combined lightoutput.

In some embodiments, the pattern is configured to cover a substantiallycontiguous portion of the target substrate. For example, a contiguoushalf, third, or other fraction of the target substrate may be covered ina continuous manner. In some embodiments the entire, target surface maybe covered. FIG. 8A illustrates a top view of a target substrate 810such as an LED die, onto which a light-converting material such asphosphor has been applied in a substantially contiguous pattern 815. Aportion 817 remains substantially un-patterned. Subsequent layers oflight-converting material may be applied overtop of portions of thepattern 815 and/or portions of the un-patterned portion 817.

In some embodiments, the pattern is configured to cover a predeterminedportion of the target substrate in a substantially non-continuouspattern. For example, the pattern may be deposited in a rectangularpattern, circular pattern, checkerboard pattern, meandering pattern, orother pattern comprising plural regions of patterned light-convertingmaterial intermixed with plural regions without said light-convertingmaterial. The regions without light-converting material may be patternedwith another light-converting material, or they may remain substantiallyfree, of patterned light-converting material. FIG. 8B illustrates a topview of a target substrate 820 such as an LED die, onto which alight-converting material such as phosphor has been applied in a.‘checkerboard’ pattern 825. A portion of the substrate 820 complementaryto the ‘checkerboard’ 825 remains substantially unpatterned. Acheckerboard pattern comprising square features will cover 50% of thetarget substrate. By also patterning parts of the unpatterned portions,a greater amount of the target substrate 820 may be covered withlight-converting material. Similarly, a lesser amount of the targetsubstrate 820 may be covered with light-converting material byrefraining from patterning parts of the “checkerboard” 825.

In some embodiments, both the size and location of portions of thepattern may be varied, for example statistically, in order to avoid moreeffects or other optical artifacts arising from placement of thelight-converting material. FIG. 8C illustrates a top view of a targetsubstrate 830 such as an LED die, onto which a light-converting materialsuch as phosphor has been applied in a pattern 835 having features ofvariable size and positioned in a substantially irregular manner. Aportion of the substrate 830 complementary to the pattern 835 remainssubstantially unpatterned. Statistical algorithms for covering a desiredportion of the target substrate with light-converting material, suchthat the pattern displays feature sizes falling within a desired rangeand commensurate with a desired statistical distribution, and/or thepattern displays spacings between features falling within a desiredrange and commensurate with a desired statistical distribution, would bereadily understood by a worker skilled in the art. Randomized orpseudo-randomized patterns may be generated as needed, or pre-generatedand drawn from a database of patterns as needed.

Placement-Tolerant and Placement-Sensitive Patterns

In embodiments of the present technology, patterns of light-convertingmaterial may be applied to the target substrate via one or morepredetermined pattern templates. A pattern template may be employed tofacilitate conversion of light of one or more light-emitting elements byapplying light-converting material provided by a pattern template thatis adequately positioned and oriented relative to the corresponding oneor more light-emitting elements. By rotating the pattern template, theapplied pattern of light-converting material can be rotated. By movingthe pattern template relative to the target substrate, the pattern oflight-converting material can be applied to a different section of thetarget substrate.

As an example, a pattern template can be employed in combination with aset of corresponding instructions for energizing a donor substrate at apredetermined set of locations in accordance with certaincharacteristics of the pattern template. By displacing and/or rotatingthe target substrate relative to the donor substrate and patterntemplate, the applied pattern, can be correspondingly displaced and/orrotated. By adjusting the set of instructions in accordance with alinear transformation, the pattern template itself may be translatedand/or rotated relative to the donor substrate.

In some embodiments, the pattern template has a larger area than thetarget substrate. In this case, the pattern could be applied only wherethe pattern template, overlies the target substrate. In someembodiments, a machine vision or similar system may be used to locatethe edges of the target substrate, so that light-converting material isconserved and effectively used, and is not applied off of the substrateand onto an operating area or optically inactive carrier surfaceassociated with the target substrate. In some embodiments, thelight-converting material may be applied off of the target substrate,for example onto an operating area surface or optically inactivecarrier. Excess deposits from such application may be recycled or reusedto limit wastage of light-converting material.

In some embodiments, the pattern template has a larger area than arelevant portion of the target substrate associated with alight-emitting element. For example, when the target substrate comprisesor is associated with dilute light-emitting elements, relevant portionsmay include regions directly above such light-emitting elements,possibly along with directly adjacent regions. In this regard, it isnoted that light-converting material may capture and convert rays oflight even if they are not directly above a light-emitting element, forexample in embodiments comprising light diffusers and/or non-collimatedlight sources. Such a pattern may be deposited in accordance with theentire pattern template, provided that the pattern template does notfall off the edge of the target substrate.

Although the pattern template may be larger than the target substrate,or relevant portion thereof, features of the associated pattern aretypically substantially smaller than a corresponding target substrate orrelevant portion thereof.

Patterns applied via pattern templates may exhibit a predeterminedamount of placement sensitivity. Placement sensitivity is generallydefined as the amount by which a predetermined aspect of resultantlight, such as chromaticity of combined light from light-emittingelements and light-converting material, is affected by variations inalignment and/or rotation of a pattern, as applied by a patterntemplate, relative to the target substrate or portion or portionsthereof. For example, chromaticity generally varies with the proportionof target substrate, or relevant portion thereof, covered by apredetermined light-converting material. Placement sensitivity may thusbe related to the amount by which this proportion changes as the patternalignment and/or rotation varies. This type of placement sensitivity isreferred to herein as proportion placement sensitivity, and typicallyrelates to a pattern of a template which is oversized relative to thetarget, substrate or relevant portion thereof.

If placement sensitivity of a pattern is relatively low, the pattern maybe referred to as being placement-tolerant. If placement sensitivity ofa pattern is relatively high, the pattern may be referred to as beingplacement sensitive.

It is also noted that placement sensitivity may depend on the type ofalignment variation. Thus, a pattern may be sensitive to horizontaldisplacement, vertical displacement, rotation, or a combination thereof.Furthermore, a pattern may be placement sensitive when subjected to onetype of alignment variation and placement tolerant when subjected toanother. Furthermore, in some embodiments, a pattern may beplacement-tolerant when subjected to displacement within a first rangeand placement-sensitive when subjected to displacement beyond said firstrange, or vice-versa.

In embodiments of the present technology, placement-tolerant patternsmay be used to facilitate manufacturing, since predeterminedcharacteristics of the combined light may be substantially achieved evenif the target substrate and pattern template are potentially subjectedto misalignment during manufacturing. Such misalignment may occurrandomly due to limitations in mechanical registration of the targetsubstrate in the operating area, for example, or due to vibrations of acontinuous roller target substrate feed, for example of a web-fedapparatus.

In embodiments of the present technology, placement-sensitive patternsmay be used to facilitate improved manufacturing, by providing a meansfor controlling aspects of resultant light, such as chromaticity, of amanufactured product. For a proportion placement sensitive pattern, theplacement-tolerant pattern may be configured such that varying placementof the pattern on the target substrate by a predetermined amount willresult in a corresponding and predictable variation in the amount oflight-converting material in the pattern which is operatively coupled tothe light-emitting elements associated with the target substrate. Forexample, the amount of light-converting material may vary linearly witha horizontal displacement in a predetermined manner. This may in turnresult in a corresponding and predictable variation in characteristics,such as chromaticity, of the combined light. In this embodiment,characteristics such as chromaticity of the combined light may becontrollably adjusted by adjusting alignment between a pattern and thetarget substrate and/or light-emitting elements or elements associatedtherewith.

In some embodiments, a machine vision system may be used to adjustrelative alignment of the pattern template and target substrate, therebyadjusting amount of light-converting material deposited for a proportionplacement sensitive pattern. Light-converting material may thus bedeposited in the same pattern for a batch of target substrates, but withplacement variations used to control chromaticity (for example when usedalong with pre-characterization), rather than a more computationallyintensive process of re-adjusting the entire pattern for each targetsubstrate.

Examples of patterns of varying, proportion placement sensitivity areillustrated in FIGS. 9 and 10. FIG. 9 illustrates a checkerboard patterntemplate 910 located overtop of a target substrate or portion thereof915, such as an LED chip. FIG. 9 also illustrates first and secondradial pattern templates 920, 930, located overtop of similar targetsubstrates or portions thereof 925, 935, respectively. A pattern oflight-converting material is formed in accordance with the patterntemplates 910, 920, 930 at least where those templates overlie thecorresponding target substrates or portions 915, 925, 935, respectively.Where the templates extend beyond the boundaries of their underlyingtarget substrates, the pattern is not formed, since there is nosubstrate on which to deposit material. Where the target, substrate isassociated with spaced-apart light-emitting elements, the patterns mayoptionally extend beyond the boundaries of the light-emitting elements.

Depending on the embodiment, pattern templates may be bigger than thetarget substrates to facilitate placement tolerance. For example,pattern templates 910, 920, 930 cover a wider surface area than thetarget substrates or portions 915, 925, 935. Thus, for example, if thecheckerboard pattern template 910 is shifted upward, a top portion ofthe light-converting material is no longer associated with thelight-emitting element underneath. However, a bottom portion oflight-converting material, of about the same amount, is introduced, andthe overall amount of patterned light-converting material issubstantially unchanged. The pattern template 910 is thusplacement-tolerant under left, right, upward or downward lateraldisplacement within a plane parallel to the target substrate 915. Asanother example, if the pattern templates 920 or 930 are rotated, theamount of light-converting material overtop and/or proximate to anassociated target substrate 925 or 935 changes only by a limited amount.It is noted that cylinder symmetric pattern templates, for example, asolid disc, or with concentric rings (neither illustrated) arecompletely tolerant to rotation. If the radial pattern template 920 isshifted, upward or downward, the amount of light converting materialdeposited may change corresponding to an up-down sensitive pattern. Ifthe radial pattern template 920 is shifted to the left or right, theproportion of target substrate 925 covered by light-converting materialwill remain constant until the perimeter of the light convertingmaterial will pass post the corner of the light emitting element. Thusthe pattern template 920 corresponds to a left-right placement-tolerantpattern. Moving to a radial pattern template with eight segments atleast partially improves tolerance against pattern translation inup-down or left right movement and rotation. The radial pattern template930 corresponds to a substantially more placement-sensitive patternunder displacements, as no axis is immediately identified such thatsubstantial displacement along said axis leaves unchanged the proportionof target substrate 935 covered by pattern.

FIG. 10 illustrates example pattern templates 1010 and 1030 forproviding patterns which are placement-sensitive under certainconditions. For example, the pattern template 1010 comprises a leftregion 1015 and a right region 1020, each of which has a size largerthan that of a corresponding target substrate or region thereof 1025. Adifferent amount of light-converting material is substantially uniformlypatterned via the left region 1015 in comparison to the right region1020. By shifting the pattern template 1010 leftwards or rightwards, anamount of light-converting material applied to the target substrate orregion thereof 1025 is thus controllable. However, the pattern oftemplate 1010 is placement-tolerant in the up-down direction, regardlessof left-right displacement.

The pattern template 1030 comprises a first region 1035 and a secondregion 1040, wherein a different amount of light-converting material issubstantially uniformly patterned via the first region 1035 incomparison to the second region 1040. Starting from the illustratedposition of the pattern template 1030 over top of the target substrateor region thereof 1045, leftward or rightward displacement of thepattern template 1030 by an incremental amount x will result in acorresponding change in the amount of area of the target substrate orregion thereof 1045 being patterned via the first region 1035 and thesecond region 1040. For example, the first region 1035 may correspond tono application of light-converting material and the second region 1040may corresponds to full application of light-converting material. For upto a predetermined amount of left or right displacement, the amount oftarget substrate or region thereof 1045 which is patterned via the firstor second region changes in direction proportion to the amount of leftor right displacement. Moreover, the constant of proportionality may betuned by up displacing the pattern within its plane in the directionorthogonal to said left-right displacement. As long as the patterntemplate 1030 is not displaced from the illustrated position in theleft-right direction, it also corresponds to a substantiallyplacement-tolerant pattern in the up-down direction.

The degree by which the pattern of template 1030 is placement-tolerantis related to the amount by which the central axes 1037 and 1042 of thetemplate cross the center point of the target substrate 1045. Asillustrated, the vertical axis 1037 passes through the center point, sothat the pattern is placement-tolerant under vertical translation.Conversely if it was the horizontal axis 1042 passing through the centerpoint then the pattern would be placement-tolerant under horizontaltranslation. If neither axis 1037 or 1042 passes through the centerpoint, the pattern would be placement-sensitive under both vertical andhorizontal translation. Axes of symmetry thus play a role in identifyingplacement sensitivity of certain patterns.

More generally, proportion placement sensitivity for a pattern of onetype of light-converting material can be evaluated as follows. Thepattern template can be associated with a two-dimensional surface S onwhich a scalar field is defined. The scalar field represents, for eachlocation on S, the amount of light-converting material to be patternedat that location. The scalar field may take on binary values in anembodiment where the light-converting material is either applied to auniform thickness or not applied. Next, define a closed curve C,representing the size and shape of the target substrate or relevantportion thereof, such as an LED. The closed curve C is initially locatedat an arbitrary point on the surface S, but can be translated and/orrotated under arbitrary transformations T. The location of the closedcurve C on the surface S under transformation T is denoted C(T). Definethe intersection of the surface S and the closed curve C(T) as asub-surface S_(C)(T). The proportion of light-converting materialpatterned on the target substrate is then represented by a surfaceintegral of the scalar field over the entire sub-surface S_(C)(T).Placement sensitivity can then be evaluated as the rate of change ofS_(C)(T) with respect to a given variation in T. If the rate of changeis near zero, the pattern is placement tolerant for the given variationin T. It is expected that proportion placement sensitivity for patternsof plural types of light-converting materials may be similarly evaluatedby taking a surface integral over an appropriate vector field.

Single and Multiple Layers

In some embodiments, a single, typically patterned, layer oflight-converting material may be applied to the target substrate inaccordance with the present technology. For example, a single layer ofphosphor may be deposited in a predetermined pattern onto a blue orultraviolet pump LED die, wafer, or other target substrate.

In some embodiments, plural, typically patterned, layers oflight-converting may be applied to the target substrate in accordancewith the present technology. Each layer may be applied in apredetermined sequence, in accordance with a transfer process asdescribed herein. The first layer is applied directly to the targetsubstrate. Subsequent layers are applied to the target substrate on topof previously applied layers.

In some embodiments, the target substrate may be evaluated between layerapplications. For example, chromaticity due to the combinedlight-emitting elements and light-converting material may be evaluatedafter application of one or more layers. Based on said evaluation,patterning of subsequent layers may be adjusted to achieve a desiredchromaticity, or no further layers may be applied if a satisfactorychromaticity has been reached.

In some embodiments, a fresh donor substrate, that is, a portion fromwhich light-converting material has not yet been transferred, or freshportion of a donor substrate is used for application of each pattern. Insome embodiments, a partially used donor substrate may be re-used, forexample for applying a second pattern to the same target substrate orfor applying a pattern to another target substrate, provided that thepattern is formed using portions of the donor substrate that have notbeen previously depleted of light-converting material. For example, twocomplimentary checkerboard patterns may be derived from the same donorsubstrate. As another example, the donor substrate may be displacedsimilarly to a typewriter ribbon, so that fresh portions areappropriately located where pattern transfer is to occur.

In some embodiments, plural layers of substantially the samelight-converting material may be applied to the target substrate. Byoverlapping the plural layers, the thickness of the light-convertingmaterial on selected portions of the target substrate may becontrollably adjusted, for example creating vertical stacks oflight-converting material in predetermined regions. By varying thicknessof regions of light-converting material such as phosphor, thecontribution to resultant chromaticity of these regions may becontrolled, as would be readily understood by a worker skilled in theart. In some embodiments, this provides an even higher degree of controlover chromaticity than single-layer patterning. For example, assuming a1 mm square LED, a 10 μm pattern pixel size, and 5 layers of pattern‘overwriting’. 50,000 different amounts of light-converting material maybe applied. Thus, the proportion of target substrate covered bylight-converting material in this example can be controllably variedfrom 0% to 100% in 0.002% increments.

FIG. 11A illustrates a locus 1130 of chromaticities on a 1931 CIEchromaticity diagram, which can be achieved by patterning one layer orplural layers of the same light-converting material onto a targetsubstrate. The target substrate associated with a light-emitting elementhaving a predetermined chromaticity 1110. To a first approximation, thelight-converting material absorbs light from the light-emitting elementand emits light of a different chromaticity 1120. By varying theproportion of the target substrate covered by the light-convertingmaterial and the thickness of the light converting material, differentchromaticity points along the linear locus 1130 may be achieved for thecombined, light of the light-emitting element and the light-convertingmaterial. If the thickness of the color-converting material is thickenough such that all light emitted from the light-emitting element incommunication with the color-converting dot is converted then 100%coverage results in chromaticity 1120. However, if the thickness of thecolor-converting layer is not sufficient to convert all light (light ofthe pump source leaks through) then the chromaticity space availablethrough single layer coat is limited by the chromaticity point definedby 100% coverage. In this scenario multilayer coating will then furtherextend the available chromaticity space up to 1120.

In an exemplary embodiment, three layers of light-converting materialare employed. The layer thickness may be designed such that combinationof all three layers with 100% coverage achieves chromaticity 1120 (forexample via complete absorption, and conversion of light from the pumplight source), with each individual layer absorbing a fraction of thepump light. This approach may effectively increase the chromaticityresolution while maintaining the optical resolution.

In some embodiments, plural layers of different light-convertingmaterials may be applied to the target substrate. This may be instead ofor in addition to application of plural layers of the samelight-converting material. Each different light-converting material mayhave different characteristics, such as a different emissionchromaticity. For example, different light-converting materials may bephosphors with different tight absorption and/or re-emission spectralprofiles. Use of plural layers of different light-converting materialmay facilitate achieving a desired chromaticity, a desired colorrendering index (CRI) and/or to compensate for chromaticity variationsof the light-emitting elements, light-converting materials, or acombination thereof. The layers of different chromaticity may be appliedoverlapping one another or not overlap one another or even separated byrelatively small finite spaces.

FIG. 11B illustrates a substantially triangular region 1170 ofchromaticities on a 1931 CIE chromaticity diagram, which can be achievedby patterning two different light-converting materials onto a targetsubstrate in a non overlapping fashion. The target substrate associatedwith a light-emitting element having a predetermined chromaticity 1140.To a first approximation, a first light-converting material absorbslight from the light-emitting element and emits light of a different,spectrum 1150, and a second light-converting material absorbs light fromthe light-emitting element, and emits light of another differentspectrum 1160. Assuming that no light of the pump wavelength bleedsthrough the corresponding color converter layers (100% conversion), byvarying the proportions of the target substrate covered by the first andsecond light-converting material, any chromaticity points within theregion 1170 may be achieved for the combined light of the light-emittingelement and the light-converting materials. If the light-convertingmaterial does not achieve 100% conversion, a subset of points within theregion 1170 may be achievable. If the plural light-converting materialsinteract cannibalistically, for example due to proximity and/oroverlapping of the light-converting materials, some points within theregion 1170 may not be achievable without adequately compensating forthe cannibalistic effects.

In some embodiments, plural layers of different light-convertingmaterials may be applied to the target substrate in an overlappingfashion. The target substrate is associated with one or morelight-emitting elements having a predetermined chromaticity 1140. To afirst approximation, a first light-converting material absorbs lightfrom the light-emitting element and emits light of a different spectrumhaving chromaticity 1150, and a second light-converting material absorbslight from the light-emitting element, and emits light of anotherdifferent spectrum having chromaticity 1160. The first light convertingphosphor may be deposited first and the second light converting phosphorcoated in a second step. This generates a chromaticity quadrangle havingvertices of: the pump wavelength 1140 (in regions where no phosphor isapplied), the response function of the first light converting phosphor1150 (where only the first phosphor is applied), the response functionof the second light converting phosphor 1160 (where only the secondphosphor is applied in direct communication with the pump source), andthe response function of the second phosphor on the first phosphor(where the second phosphor is coated onto the first phosphor).

In some embodiments comprising plural layers of differentlight-converting materials applied to the target substrate, differentlight-converting materials may be deposited in a non-overlapping manner.For example, the target substrate may be divided into contiguous ornon-contiguous regions, each region covered by only one type oflight-converting material. By avoiding overlapping of light-convertingmaterials, undesired effects such as cannibalistic effects, due tocombination of different light-converting materials, can be controlledor avoided.

As would be readily understood by a worker skilled in the art, theabsorption and emission bands of certain light-converting materials suchas phosphors can be relatively close and even overlapping. For instance,a YAG:Ce yellow phosphor may absorb at 420 to 500 nanometers wavelengthand emit at 500 to 650 nanometers, predominantly in the yellow region ofthe spectrum (thus the yellow tint). Therefore, for example, if anorange/red emission is desired to boost the long wavelength tail, thisphosphor may absorb at 450 to 600 nanometers. This overlapssubstantially the emission of the yellow phosphor, removing some of thatemission from the final spectrum. This phenomenon may be readilyunderstood by a worker skilled in the art, for example in relation toradiation trapping and cannibalization. Such cannibalisation can beundesirable as it reduces the efficiency of the system. By patterningthe deposits in small dots as described herein, regions of differentphosphors, which would otherwise exhibit cannibalization aresubstantially removed from their neighbours, thereby reducing orinhibiting such cannibalisation. By providing a spaced-apart andnon-overlapping arrangement, plural light-converting materials may beutilized, even if those materials would not otherwise be compatible ifthey were present in a single mixture due to cannibalization. This mayallow for use of plural phosphors or other light-converting materialswith much closer emission peaks than in other prior art solutions,allowing a more uniform final emission spectrum. Benefits can be foundboth in improved luminous efficacy of such a device (withoutreabsorption of converted light) and in improved Color Rendering IndexCRI due to better approximation of spectral composition of a black bodylight source.

In some embodiments comprising plural layers of differentlight-converting materials applied to the target substrate, differentlight-converting materials may be deposited in an at least partiallyoverlapping manner.

FIGS. 12A to 12C illustrate examples of target substrates applied withnon-overlapping or overlapping patterns of light-converting material.FIG. 12A illustrates a top view of a target substrate 1210 such as ablue LED. A first region 1212 of the target substrate 1210 has beencontiguously patterned with yellow phosphor, and a second region 1214 ofthe target substrate 1210 has been contiguously patterned with anothermaterial such as red phosphor or red quantum dot material. FIG. 12Billustrates a top view of the target substrate 1210, wherein anotherportion 1216 of the target substrate 1210 is patterned with anotherlight-converting material. In FIGS. 12A and 12B, none of the differentregions 1212, 1214, 1216 overlap. In contrast, FIG. 12C illustrates topand side views of a target substrate 1220 applied with a first layer1222 of light-converting material over its entirety, and a second layer1224 of light-converting material over a portion of the first layer1222. Optionally, the first layer 1222 may cover only a portion of thetarget substrate 1220, and/or the second layer 1224 may cover the entirefirst layer 1222 and optionally also all of the target substrate 1220.Different portions of the target substrate, for example corresponding todifferent LEDs, may be patterned differently, for example in order toindividually tune, chromaticity of each portion of the substrate.

Depending on the embodiment two or more layers of differentlight-converting materials with corresponding emission spectra may becombined to provide a predetermined emission spectrum and/orcolor-rendering index (CRI) of the combined, light. Depending on theembodiment, light-converting material, may be disposed, to aid inmitigation of cannibalization of light, therein and/or in the provisionof combined light with a smooth emission spectrum that exhibits avariation with wavelength that may be at, above or below a predeterminedlevel. For example. FIG. 16 illustrates emission spectra 1610 ofdifferent combinations of light-emitting elements and light-convertingmaterials. As can be seen, the emission spectrum 1620 does not have aspronounced a valley in the 500 nm region as the spectrum 1610.

In some embodiments, and as described above, two differentlight-converting materials are applied to the target substrate. Thisfacilitates chromaticity variation of the combined light due to thelight-emitting elements and light-converting materials in apredetermined two-dimensional region of the CIE color diagram. In someembodiments, three or more different light-converting materials may beapplied to the target substrate. This facilitates chromaticity variationof the combined light in another two-dimensional region of the CIE colordiagram. In some embodiments, this region may generally be described asbeing contained within the convex polygon defined by the chromaticitypoints describing the light-emitting elements and the light-convertingmaterials.

In some embodiments wherein three or more different light-convertingmaterials are applied to the target substrate, some chromaticities maybe obtainable via two or more different chromaticity solutions, whereineach chromaticity solution represents application of one or morelight-converting materials over a specified proportion of the targetsubstrate. In other words, an under-constrained problem is created,whereby more degrees of freedom (proportions of the target substratecovered by each light-converting material) are available than arerequired for obtaining one or more chromaticities. In this case, achromaticity solution may be selected, from the plural availablesolutions, based on one or more other criteria. For example, a solutionmay be selected which also results in combined light output having closeto a desired luminous flux output or color rendering index. Selectionmay be performed by a mathematical optimization algorithm, lookup table,or the like.

Post-Transfer Processes

In some embodiments, a baking and/or annealing process is performedafter transfer of the light-converting materials. Such a process may beused to more permanently affix the light-converting materials to thetarget layer, to cure binder materials and adhesives, reflow layers,seal surfaces, level surfaces and the like.

Apparatus

Aspects of the present technology relate to an apparatus for couplingone or more light-emitting elements with a light-converting material.The apparatus generally comprises an operating area configured toreceive a target substrate and a donor substrate, a laser configured toenergize one or more selected locations of the donor substrate locatedin the operating area, and a motion system configured to controllablyalign the laser with the one or more selected locations forenergization.

Embodiments of the present technology may utilize a thermal laserimaging head such as provided in the Kodak Squarespot™ product line, orthe alternately Agfa Excalibur™ product line. For example, a laserimaging head with 2400 dpi resolution may provide sufficient opticalresolution and addressability with a pixel size of approximately 10 μmand may also provide sufficient optical output power to achieve transferat high throughput levels. An example laser may have 20 W nominal powerand/or provide infrared light at 830 nm or longer. Example thermalimaging systems may be adapted to image substrates wrapped around drums,or substrates laid on a flat surface.

Embodiments of the present technology utilize a laser with emissionspeaks in the near infrared spectrum, for example near 830 nm.Embodiments of the present technology may utilize lasers with emissionpeaks at other wavelengths, for example at 1064 nm as provided by NdYAGlasers, 980 nm provided by InP lasers, about 1310 nm or 1530 to 1560 nmor other wavelengths as provided by Erbium doped fiber lasers, orquantum cascade or other lasers. Embodiments of the present technologyassociated with such lasers typically utilize a thermally activatedprocess for transfer of light-converting material. Equipmentincorporating such lasers and capable of operating same with highresolution and high optical output is readily available in the industry.

In some embodiments transfer of light-converting material may beinitiated by a blue near UV or UV laser, or other laser, for example. Inthis case, the transfer process may shift from a thermally activatedprocess to a photon-activated process, as described herein. In oneembodiment a near UV imaging system such as the AGFA Galileo™ CTP may beutilized. The Agfa Galileo imaging system provides 2400 dpi at 410 nmwavelength. In some embodiments a laser may be configured to utilizehigher harmonics of the NdYAG wavelength of 1064 nm such as frequencydoubled 532 nm, tripled 355 nm or quadrupled 256 nm wavelengths. Someembodiments may also utilize deep LTV emission as supplied by excimerlasers, for example.

In some embodiments, the apparatus comprises a motion control system,such as a robotic actuation system, configured to move the laser and/ordonor and target substrates with adequate accuracy for patterning.Various motion control systems, enabled by computer automationequipment, may be utilized as would be readily understood by a workerskilled in the art. Various commercially available systems such as theKodak Squarespot™ product line incorporate motion control systems.

In some embodiments, the apparatus comprises a registration system, suchas a machine vision system or mechanical registration system, which isconfigured to ensure registration of the target substrate and/or donorsubstrate prior to patterning via laser. The registration system mayfurther be configured to register a position of the target substraterelative to a baseline coordinate system, so that physical offsetsbetween the target substrate and the baseline coordinate system may becompensated for, thereby reducing potential for pattern misalignment andhence improving accuracy of chromaticity or other aspect of theresulting product.

The technology will now be described with reference to specific example.It will be understood that the example is intended to describeembodiments of the technology and are not intended to limit thetechnology in any way.

Example

The present example illustrates tunability of white light LEDsmanufactured in accordance with an embodiment of the present technology,in comparison to the prior art. FIG. 13A illustrates an example binningdiagram used by a commercial LED manufacturer. Each region of thebinning diagram corresponds to a region of the CIE 1931 (x,y)chromaticity diagram. In a typical manufacturing step, LEDs are testedto determine their chromaticity associated with a corresponding bin.FIG. 13B displays the ANSI C378.77 tolerance specification for generalillumination solid-state light sources, on a CIE 1931 (x,y) chromaticitydiagram. Each quadrangle on the diagram represents a range ofchromaticities that adequately correspond to a nominal correlated colourtemperature (CCT) at the center of the quadrangle. A 7-step MacadamEllipse is also illustrated for each nominal CCT. FIG. 13C displays ahypothetical chromaticity distribution of a batch of blue pump LEDs withwhite phosphor coating, produced in accordance with a prior artmanufacturing process, assuming sigma 1.5% process variation and about 2nm wavelength variation in wavelength of light from the blue LEDs. Suchprior art manufacturing methods can provide predetermined consistencyamong binned devices on the order of a 7 step MacAdam ellipse orapproximately Duv 0.012. Here the Duv refers to the 1976 CIEChromaticity Diagram (not illustrated), where the sum of the differencesof each coordinate of the corners of the region of interest is 0.012.That is, └(u′1−u′2)²+(v′1−v′2)²┘^(1/2)=0.012, where u′1 v′1 and u′2 v′2are chromaticity coordinates.

FIG. 13D illustrates the chromaticity tunability, on a CIE 1931 (x,y)chromaticity diagram, of white phosphor coated blue. LEDs manufacturedin accordance with an exemplary embodiment of the present technology,assuming a fixed chromaticity for the LEDs and phosphor source. Assumingthe amount of phosphor coating can be adjusted from 0% to 100% inincrements of 0.1%, a tunability resolution of Duv 0.0003 can beachieved. Adjacent squares on the locus 1350 differ by 0.1% in theamount of phosphor coating applied. The locus 1350 passes through the6500 K chromaticity point 1362 on the black body curve 1360. Whenchromaticity of the LEDs and/or phosphor source vary, evaluation andfeedback mechanisms may be used to adjust the amount of phosphorcoating, thereby achieving tight manufacturing tolerances.

It is obvious that the foregoing embodiments of the technology areexamples and can be varied in many ways. Such present or futurevariations are not to be regarded as a departure from the spirit andscope of the technology, and all such modifications as would be obviousto one skilled in the art are intended to be included within the scopeof the following claims.

What is claimed is:
 1. A method for coupling one or more light-emittingelements with a light-converting material, comprising: a) providing atarget substrate, the target substrate associated with the one or morelight-emitting elements; b) providing a donor substrate proximate to thetarget substrate, the donor substrate comprising the light-convertingmaterial and configured to transfer a portion of the light-convertingmaterial to the target substrate upon a predetermined energization of acorresponding portion of the donor substrate; c) measuring one or morefirst optical properties of the one or more light-emitting elements; d)determining one or more desired optical, properties of a combination ofthe one or more light-emitting elements and the light-convertingmaterial; e) determining a pattern of the light-converting material tobe transferred to the target substrate based on the one or more desiredoptical properties and the one or more first optical properties; and f)controllably energizing one or more locations of the donor substrateselected in accordance with the pattern, thereby transferring thelight-converting material from the donor substrate to the targetsubstrate at said one or more selected locations.
 2. A method forcoupling one or more light-emitting elements with a light-convertingmaterial, comprising: a) providing a target substrate, the targetsubstrate associated with the one or more light-emitting elements; b)providing a donor substrate proximate to the target substrate, the donorsubstrate comprising the light-converting material and configured totransfer a portion of the light-converting material to the targetsubstrate upon a predetermined energization of a corresponding portionof the donor substrate; c) measuring one or more first opticalproperties of the one or more light-emitting elements; d) measuring oneor more second optical properties of the donor substrate; e) determiningone or more desired optical properties of a combination of the one ormore light-emitting elements and the light-converting material; f)determining a pattern of the light-converting material to be transferredto the target substrate based on the one or more desired opticalproperties, the one or more first optical properties and the one or moresecond optical properties; and g) controllably energizing one or morelocations of the donor substrate selected in accordance with thepattern, thereby transferring the light-converting material from thedonor substrate to the target substrate at said one or more selectedlocations.
 3. The method according to claim 1, wherein the targetsubstrate comprises the one or more light-emitting elements, or whereinthe target substrate comprises an optically transmissive material forpositioning proximate to the one or more light-emitting elements.
 4. Amethod for coupling one or more light-emitting elements with alight-converting material, comprising: a) providing a target substrate,the target substrate associated with the one or more light-emittingelements; b) providing a donor substrate proximate to the targetsubstrate, the donor substrate comprising the light-converting materialand configured to transfer a portion of the light-converting material tothe target substrate upon a predetermined energization of acorresponding portion of the donor substrate; c) controllably energizingone or more selected locations of the donor substrate, therebytransferring the light-converting material from the donor substrate tothe target substrate at said one or more selected locations; wherein,after transferring the light-converting material from the donorsubstrate to the target substrate, the method further comprises: d)providing a second donor substrate proximate to the target substrate,the second donor substrate comprising a second light-converting materialand configured to transfer a second portion of the secondlight-converting material to the target substrate upon a secondpredetermined energization of a second corresponding portion of thedonor substrate; and e) controllably energizing one or more secondselected locations of the donor substrate, thereby transferring thesecond light-converting material from the second donor substrate to thetarget substrate at said one or more second selected locations.
 5. Themethod according to claim 4, wherein the one or more selected locationsform a pattern covering a predetermined proportion of the targetsubstrate, said predetermined proportion selected based on one or moredesired optical properties of a combination of the one or morelight-emitting elements and the light-converting material.
 6. The methodaccording to claim 5, wherein the pattern is configured such that thepredetermined proportion is substantially unchanged under up to apredetermined amount of alignment variation between the pattern and theone or more light-emitting elements.
 7. The method according to claim 5,wherein the pattern is configured such that the predetermined proportionvaries in a predetermined manner with alignment variation between thepattern and the one or more light-emitting elements, and where saidalignment variation is selected to control said predeterminedproportion.
 8. The method according to claim 5, wherein the pattern is aregular pattern, a pseudo-randomized pattern, or a randomized pattern,and a feature of the pattern has a nominal shape selected from a groupconsisting of polygons, rectangles, squares, parallelograms, trapezoids,ellipses, circles, and ovals.
 9. The method according to claim 5,wherein the pattern is configured to cover a first predeterminedproportion of a first portion of the target substrate and the pattern isconfigured to cover a second predetermined proportion of a secondportion of the target substrate, the first predetermined proportiondifferent from the second predetermined proportion.
 10. The methodaccording to claim 4, wherein at least one of the one or more secondselected locations at least, partially overlaps, at least one of the oneor more selected locations.
 11. The method according to claim 4, whereinat least one of the second selected locations and the one or moreselected locations are free from overlaps.
 12. The method according toclaim 4, wherein the second light-converting material and thelight-converting material are one of nominally equal and different. 13.The method according to claim 2, wherein energizing of the one or moreselected locations is performed by a laser.
 14. A lighting devicemanufactured according to claim 4.